The present invention relates to devices which make it possible to apply threads on supports, particularly supports of plastic material or rubber, these devices permitting for example, the production of reinforcement plies, particularly reinforcement plies for pneumatic tires. In particular, the invention relates to the devices which make it possible to apply these threads while imparting to them a sinuous shape.
Devices which make it possible to apply threads on a support while imparting a sinuous shape to them are described, for example, in the following Patents or patent applications: French 2 042 859. French 2 325 497, French 2 501 126, Soviet Union 704 816, PCT 81/1151.
These devices have at least one of the following drawbacks:
(a) complicated nature of the devices giving rise to frequent breakdowns or incurring costly and frequent maintenance;
(b) lack of precision in the placing of the threads, so that the plies obtained have a heterogeneous geometry and therefore have physical characteristics which vary along their lengths.
The object of the invention is to avoid these drawbacks. Therefore, the device in accordance with the invention which makes it possible to apply at least one thread onto the surface of a support is characterized by the following features:
(a) it has two clamps arranged in an invariable order in a direction called the "direction of advance", the first clamp being called the "front clamp" and the second clamp being called the "rear clamp";
(b) the device comprises means which make it possible to open and close these clamps in such a manner that they are without contact with the support and the thread when they are open and that they are in contact with the support and the thread when they are closed;
(c) the arrangement of the front clamp is such that said clamp experiences practically only movements capable of opening or closing it;
(d) the device has means which make it possible to displace the rear clamp in the direction of advance when it is closed, so as to cause the support and the thread to advance in said direction, the rear clamp then moving away from the front clamp, which is open;
(e) the device comprises means which make it possible to displace the rear clamp in the direction opposite the direction of advance when said clamp is open, the rear clamp then approaching the front clamp which is closed;
(f) the device has means which make it possible to displace the thread in directions transverse to the direction of advance, the front clamp being arranged between said means and the rear clamp, these means being so arranged that upon this transverse displacement:
the portion of thread displaced extends from the rear clamp to upstream of the front clamp;
the portion of thread displaced is not in contact with the support;
the front clamp is open and the rear clamp closed.
The invention also concerns the process carried out in this device. This process, which makes it possible to apply at least one thread to the surface of a support, is characterized by the following features:
(a) two clamps are used which are arranged in an invariable order in one direction, called the "direction of advance",
the first clamp being referred to as the "front clamp" and the second clamp being referred to as the "rear clamp";
(b) when the clamps are opened they are not in contact either with the support or with the thread and when these clamps are closed they are in contact both with the support and with the thread;
(c) the front clamp is caused to experience practically only movements which are capable of opening or closing it;
(d) after having closed the rear clamp, it is displaced in the direction of advance in such a manner as to cause the support and the thread to advance in said direction, the rear clamp moving away from the front clamp which has been previously open;
(e) after having opened the rear clamp, it is displaced in the direction opposite the direction of advance so as to bring the rear clamp towards the front clamp which has been previously closed;
(f) after having opened the front clamp and closed the rear clamp, the thread is displaced in directions transverse to the direction of advance in such a manner that the portion of thread displaced extends from the rear clamp to upstream of the front clamp without the portion of thread displaced being in contact with the support.
The invention also concerns assemblies obtained with this device and process, these assemblies being, in particular, reinforcing plies.
The invention also concerns a reinforcing ply having reinforcement threads applied on a support, said ply being characterized by the following features:
(a) it comprises a plurality of threads over its width;
(b) the threads have a sinuous shape with vertices;
(c) the amplitude of the undulation of each thread is less than the width of the ply;
(d) for each thread the variation in the displacement ratio T is at most equal to 5% plus or minus with respect to any nominal value T.sub.n, the displacement ratio being defined by the relationship: EQU T=L/D
L being the recti/linear distance between two successive vertices and 2D being the recti/linear distance between two vertices connected by the thread via another vertex.
The reinforcing plies in accordance with the invention are used to produce various articles, for instance tubes, membranes, belts and pneumatic tires.
The expression "thread" is to be taken in a very general sense. A thread may be a "single thread" formed, for instance, of one or more filaments. When this single thread is formed of a single filament it is referred to as a "monofilament" and when the single thread is formed of a plurality of filaments it is called a "multifilament."
A thread may furthermore itself be an assembly of single threads. By way of example, such an assembly is referred to as a "plied thread" when it is formed of a plurality of single threads connected by a single twisting operation, while such an assembly is referred to as a "cabled thread" when it is formed of several threads at least one of which is a plied thread united by one or more twisting operations.
The invention will be easily understood by means of the non-limitative examples which follow and the diagrammatic figures concerning these examples.